Toll-like receptor 2 is present in the microenvironment of oral squamous cell carcinoma

Resolution of chronic inflammation and cancer

Chronic inflammation poses challenges to effective cancer treatment. Although anti-inflammatory therapies have shown short-term benefits, their long-term implications may be unfavorable because they fail to initiate the necessary inflammatory responses. Recent research underscores the promise of specialized pro-resolving mediators, which play a role in modulating the cancer microenvironment by promoting the resolution of initiated inflammatory processes and restoring tissue hemostasis. This review addresses current insights into how inflammation contributes to cancer pathogenesis and explores recent strategies to resolve inflammation associated with cancer.

The HPV viral regulatory mechanism of TLRs and the related treatments for HPV-associated cancers

Infection with human papillomavirus (HPV) typically leads to cervical cancer, skin related cancers and many other tumors. HPV is mainly responsible for evading immune tumor monitoring in HPV related cancers. Toll like receptors (TLRs) are particular pattern recognition molecules. When the body is facing immune danger, it can lead to innate and direct adaptive immunity. TLR plays an important role in initiating antiviral immune responses. HPV can affect the expression level of TLR and interfere with TLR related signaling pathways, resulting in sustained viral infection and even carcinogenesis. This paper introduces the HPV virus and HPV related cancers. We discussed the present comprehension of TLR, its expression and signaling, as well as its role in HPV infection. We also provided a detailed introduction to immunotherapy methods for HPV related diseases based on TLR agonists. This will provide insights into methods that support the therapeutic method of HPV related conditions with TLR agonists.

Toll-like receptors in health and disease

Toll-like receptors (TLRs) are inflammatory triggers and belong to a family of pattern recognition receptors (PRRs) that are central to the regulation of host protective adaptive immune responses. Activation of TLRs in innate immune myeloid cells directs lymphocytes to produce the most appropriate effector responses to eliminate infection and maintain homeostasis of the body's internal environment. Inappropriate TLR stimulation can lead to the development of general autoimmune diseases as well as chronic and acute inflammation, and even cancer. Therefore, TLRs are expected to be targets for therapeutic treatment of inflammation-related diseases, autoimmune diseases, microbial infections, and human cancers. This review summarizes the recent discoveries in the molecular and structural biology of TLRs. The role of different TLR signaling pathways in inflammatory diseases, autoimmune diseases such as diabetes, cardiovascular diseases, respiratory diseases, digestive diseases, and even cancers (oral, gastric, breast, colorectal) is highlighted and summarizes new drugs and related clinical treatments in clinical trials, providing an overview of the potential and prospects of TLRs for the treatment of TLR-related diseases.

Role of toll-like receptor in the pathogenesis of oral cancer

Toll-like receptors are important molecules of innate immunity. They are known as pattern recognition receptors. They recognise certain molecules known as pathogen-associated molecular pattern on a pathogen and release chemicals that causes inflammation. Toll-like receptors (TLR) help in the removal of the infected cell and thus stop the spread of infection and are being studied for their association with cancer. Oral carcinoma has emerged as a major problem of our country today; it is found ranks first in men and third in women. Toll-like receptors have been implicated in the development of cancer. Certain polymorphisms in toll-like receptor can make a cell more susceptible to develop oral cancer. The identification of toll-like receptors and the different genotypes that are involved in the development of cancer can be utilised for using them as biomarkers of the disease. The study revealed that toll-like receptors like TLR7 and TLR5 are found to have a role in suppression of oral cancer while toll-like receptors like TLR4 and TLR2 are found to be associated with the progression of oral cancer. Toll-like receptors can turn out as important target molecules in the future in designing therapeutic strategies for oral cancer.

Toll-like receptor-guided therapeutic intervention of human cancers: molecular and immunological perspectives

Toll-like receptors (TLRs) serve as the body's first line of defense, recognizing both pathogen-expressed molecules and host-derived molecules released from damaged or dying cells. The wide distribution of different cell types, ranging from epithelial to immune cells, highlights the crucial roles of TLRs in linking innate and adaptive immunity. Upon stimulation, TLRs binding mediates the expression of several adapter proteins and downstream kinases, that lead to the induction of several other signaling molecules such as key pro-inflammatory mediators. Indeed, extraordinary progress in immunobiological research has suggested that TLRs could represent promising targets for the therapeutic intervention of inflammation-associated diseases, autoimmune diseases, microbial infections as well as human cancers. So far, for the prevention and possible treatment of inflammatory diseases, various TLR antagonists/inhibitors have shown to be efficacious at several stages from pre-clinical evaluation to clinical trials. Therefore, the fascinating role of TLRs in modulating the human immune responses at innate as well as adaptive levels directed the scientists to opt for these immune sensor proteins as suitable targets for developing chemotherapeutics and immunotherapeutics against cancer. Hitherto, several TLR-targeting small molecules (e.g., Pam3CSK4, Poly (I:C), Poly (A:U)), chemical compounds, phytocompounds (e.g., Curcumin), peptides, and antibodies have been found to confer protection against several types of cancers. However, administration of inappropriate doses of such TLR-modulating therapeutics or a wrong infusion administration is reported to induce detrimental outcomes. This review summarizes the current findings on the molecular and structural biology of TLRs and gives an overview of the potency and promises of TLR-directed therapeutic strategies against cancers by discussing the findings from established and pipeline discoveries.

Association between Tissue Expression of Toll-Like Receptor and Some Clinicopathological Indices in Oral Squamous Cell Carcinoma

BACKGROUND

The oral squamous cell carcinoma (OSCC) composes about 90% of all head and neck cancers. The toll-like receptor (TLR)⁺ immune cells have potential of invasion and malignancy transformation. The aim of this study was assessment of possible associations between clinicopathological indices and TLR2 and TLR9 gene expression in OSCC.

METHODS

Forty-two OSCC samples with related healthy margins including 25 early and 17 advanced stages were gathered. The samples were classified histologically from grade I to II. The expression of TLR2 and TLR2 was evaluated by Real-time PCR. The patient's disease-free survival (DFS) and overall survival (OS) were analyzed using SPSS V.23 software.

RESULTS

The expression of TLR2 and TLR9 genes in tumor tissues (especially in grade I and II) were higher than healthy surgical margin tissue (p< 0.001). TLR9 expression in grade II was statistically significant than grade I in tumor tissue (p< 0.001). TLR9 expression in advanced stage was statistically significant in compare to early stage (p= 0.012). In advanced stage both overall survival (p= 0.029) and disease-free survival (p= 0.012) were statistically lower than early stage. The follow-up time to recurrence in advanced stage was statistically lower than early stage (p= 0.007).

CONCLUSION

Overexpression of TLRs 2, 9 play role in the pathogenesis and tumor development of OSCC and can be applied as biomarker in prognostic approaches.

Evidence of a role for interleukin-6 in anoikis resistance in oral squamous cell carcinoma

In an endeavour to understand metastasis from oral squamous cell carcinomas, we characterised the metastatic potential of a human tongue derived cell line (SCC-4 cells) and compared this phenotype to pre-cancerous dysplastic oral keratinocyte (DOK) cells derived from human tongue and primary gingival keratinocytes (PGK). We demonstrate that SCC-4 cells constitutively synthesize and release significant amounts of IL-6, a process that is enhanced by the addition of the TLR2/TLR6 agonist, Pam2CSK4. The expression of TLR2/6 and IL-6Ra/gp130 receptors was also confirmed in SCC-4 cells. Cancerous SCC-4 human tongue cells also have a classic EMT profile, unlike precancerous human tongue DOK cells. We also established that IL-6 is driving anoikis resistance in an autocrine fashion and that anti-IL-6 neutralising antibodies, anti-IL-6 receptor antibodies and anti-TLR2 receptor antibodies inhibit anoikis resistance in cancerous SCC-4 human tongue cells. The data suggest a promising role for anti-IL-6 receptor antibody and anti-TLR2 receptor antibody treatment for oral cancer.

Prognostic Significance of TLR2, SMAD3 and Localization-dependent SATB1 in Stage I and II Non-Small-Cell Lung Cancer Patients

This study aimed to explore the prognostic value of SATB1, SMAD3, and TLR2 expression in non-small-cell lung carcinoma patients with clinical stages I-II. To investigate, we evaluated immunohistochemical staining to each of these markers using tissue sections from 69 patients from our cohort and gene expression data for The Cancer Genome Atlas (TCGA) cohort. We found that, in our cohort, high expression levels of nuclear SATB1ⁿ and SMAD3 were independent prognostic markers for better overall survival (OS) in NSCLC patients. Interestingly, expression of cytoplasmic SATB1^c exhibited a significant but inverse association with survival rate, and it was an independent predictor of unfavorable prognosis. Likewise, TLR2 was a negative outcome biomarker for NSCLC even when adjusting for covariates. Importantly, stratification of NSCLCs with respect to combined expression of the three biomarkers allowed us to identify subgroups of patients with the greatest difference in duration of survival. Specifically, expression profile of SATB1^n-high/SMAD3^high/TLR2^low was associated with the best OS, and it was superior to each single protein alone in predicting patient prognosis. Furthermore, based on the TCGA dataset, we found that overexpression of SATB1 mRNA was significantly associated with better OS, whereas high mRNA levels of SMAD3 and TLR2 with poor OS. In conclusion, the present study identified a set of proteins that may play a significant role in predicting prognosis of NSCLC patients with clinical stages I-II.

Genes and pathways monotonically dysregulated during progression from normal through leukoplakia to gingivo-buccal oral cancer

Oral squamous cell carcinoma of the gingivo-buccal region (OSCC-GB) accounts for the highest cancer morbidity and mortality among men in India. It has been observed that about one-third of individuals with oral leukoplakia, a dysplastic precancerous lesion in the oral cavity, progress to oral cancer. We aimed to identify systematic transcriptomic changes as a normal tissue in the oral cavity progresses to frank OSCC-GB. Seventy-two OSCC-GB patients, from multiple hospitals, were recruited, and transcriptome analysis of tumor and adjacent normal tissue (of all patients) and adjacent leukoplakia tissue (of a subset of 25 unselected patients with concomitant leukoplakia) was performed. We have identified many differences in the transcriptomic profiles between OSCC-GB and squamous cell carcinoma of the head and neck regions. Compared to the normal/precancerous tissue, significant enrichment of ECM−receptor interaction, PI3K-Akt signaling, cytokine−cytokine receptor interaction, focal adhesion, and cell cycle pathways were observed in OSCC-GB. Using gene set enrichment analysis, we identified a profound role of interferon receptor signaling in tumor growth by activating immune evasion mechanisms. The role of tumor-infiltrating immune cells further supported the growth and immunosuppressive mechanism of tumor tissues. Some immune evasion genes—CD274, CD80, and IDO1—were found to be activated even in the precancerous tissue. Taken together, our findings provide a clear insight into the sequential genetic dysregulation associated with progression to oral cancer. This insight provides a window to the development of predictive biomarkers and therapeutic targets for gingivo-buccal oral cancer.

The effect of smoking on clinical presentation and expression of TLR-2 and CD34 in Oral lichen Planus patients: clinical and immunohistochemical study

BACKGROUND

Oral lichen planus is a chronic inflammatory disease which is considered as a potential precancerous condition. Numerous studies have confirmed that inflammation is a strong risk factor for cancer development. Smoking is associated with potentially malignant disorders of the oral and oropharyngeal mucosa. The adverse consequences of smoking in various pathologies are mediated by its effects on the immune-inflammatory system. Little is known about the influence of cigarette smoke content on the course of OLP and inflammatory response.

METHODS

Twenty oral lichen planus smoker patients, 20 oral lichen planus non-smoker patients and 20 control patients were included in this work. Pain and clinical scores were calculated for each patient. Image analysis to calculate area percent for TLR-2 and CD34 immuno-expression was performed. Data was tabulated and statistically analyzed.

RESULTS

The present study showed no statistically significant difference in clinical and pain scores between the smoker and non-smoker groups. However, there was a significant difference in area percent values for TLR-2 and CD34 immuno-expression between the smoker and the non-smoker groups.

CONCLUSION

Smoking enhanced TLR-2 and CD34 expression in OLP which are considered as inflammatory mediators and are contributing factors in the pathogenesis of oral lichen planus.

Role of Toll like receptor in progression and suppression of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most common type of head and neck squamous cell carcinoma and one of the multifactorial process that consists of most contributing factors such as tobacco smoking, chewing and alcohol consumption that altered the intracellular environment. Recent studies have shown relevance of Toll like receptor (TLR) associated with carcinogenesis. This review aim’s to explore that how TLR associates with progression and suppression of OSCC. This review is a classical review that has confined to articles published in the past 19 years (i.e. 2000-2019) and has summarized the perspective of the authors. 62 articles were reviewed and it was found that progression and suppression of OSCC is associated with different TLRs promoting tumor development and also inhibiting the progression of oral neoplasm. It was found that TLR2, TLR3, TLR4, TLR5, TLR7 and TLR9 are associated with tumor development i.e. in progression of OSCC, where as suppression of OSCC through TLR3 and TLR7. We authors would like to conclude that literature survey has indicated effective TLR’s against OSCC development and can be explored to investigate other TLRs that can be used for therapeutic purposes in near future.

Insights Into Lung Cancer Immune-Based Biology, Prevention, and Treatment

Lung cancer is the number one cause of cancer-related deaths. The malignancy is characterized by dismal prognosis and poor clinical outcome mostly due to advanced-stage at diagnosis, thereby inflicting a heavy burden on public health worldwide. Recent breakthroughs in immunotherapy have greatly benefited a subset of lung cancer patients, and more importantly, they are undauntedly bringing forth a paradigm shift in the drugs approved for cancer treatment, by introducing "tumor-type agnostic therapies". Yet, and to fulfill immunotherapy's potential of personalized cancer treatment, demarcating the immune and genomic landscape of cancers at their earliest possible stages will be crucial to identify ideal targets for early treatment and to predict how a particular patient will fare with immunotherapy. Recent genomic surveys of premalignant lung cancer have shed light on early alterations in the evolution of lung cancer. More recently, the advent of immunogenomic technologies has provided prodigious opportunities to study the multidimensional landscape of lung tumors as well as their microenvironment at the molecular, genomic, and cellular resolution. In this review, we will summarize the current state of immune-based therapies for cancer, with a focus on lung malignancy, and highlight learning outcomes from clinical and preclinical studies investigating the naïve immune biology of lung cancer. The review also collates immunogenomic-based evidence from seminal reports which collectively warrant future investigations of premalignancy, the tumor-adjacent normal-appearing lung tissue, pulmonary inflammatory conditions such as chronic obstructive pulmonary disease, as well as systemic microbiome imbalance. Such future directions enable novel insights into the evolution of lung cancers and, thus, can provide a low-hanging fruit of targets for early immune-based treatment of this fatal malignancy.

Toll-like receptors: exploring their potential connection with post-operative infectious complications and cancer recurrence

Cancer is the leading cause of death in North America. Despite modern advances in cancer therapy, many patients will ultimately develop cancer metastasis resulting in mortality. Surgery to resect early stage solid malignancies remains the cornerstone of cancer treatment. However, surgery places patients at risk of developing post-operative infectious complications that are linked to earlier cancer metastatic recurrence and cancer mortality. Toll-like receptors (TLRs) are evolutionarily-conserved sentinel receptors of the innate immune system that are activated by microbial products present during infection, leading to activation of innate immunity. Numerous types of solid cancer cells also express TLRs, with their activation augmenting their ability to metastasize. Similarly, healthy host-tissue TLRs activated during infection induce a prometastatic environment in the host. Cancer cells additionally secrete TLR activating ligands that activate both cancer TLRs and host TLRs to promote metastasis. Consequently, TLRs are an attractive therapeutic candidate to target infection-induced cancer metastasis and progression.

TLR2 deficiency enhances susceptibility to oral carcinogenesis by promoting an inflammatory environment

Inflammation is closely related to oral squamous cell carcinoma (OSCC). However, its mechanism is still obscure. Toll-like receptor 2 (TLR2) plays an important role in oral chronic inflammatory diseases, but the role of TLR2 in OSCC is unclear. Here, we investigated the expression of TLR2 expression in OSCCs and examined the potential role of TLR2 in OSCC through its association with clinicopathological features and patient outcome. We used 4-nitroquinoline 1-oxide (4-NQO) to induce a tongue cancer model in TLR2-/- and wild type (WT) mice. Histological and clinical results both indicated that TLR2 played a protective role in oral tumorigenesis. The results of a cytometric bead array (CBA) indicated that TLR2 deficiency resulted in Th1 and Th2 cytokine abnormalities, especially Th2 abnormalities. Immunohistochemistry also showed that TLR2 deficiency increases the number of tongue-infiltrating M2 macrophages. Overall, our results demonstrated that TLR2 plays an important role in the prevention of oral tumorigenesis and affects the levels of Th2 cytokines and tongue-infiltrating M2 macrophages; therefore, it may be used to prevent the development of oral cancer.

Evaluation of Toll-Like Receptor Expression with Clinicopathologic Variables in Endometrium Cancer

Objectives

Clinical evidence supports the association of toll-like receptor (TLR) with abnormal cell proliferation and cancer. In this study, we investigated the expression of TLRs 2, 4, 5, and 6 in healthy endometrium and endometrium cancer to study the relationship of these receptors' expression with carcinogenesis.

Methods

Patients who had undergone a hysterectomy owing to endometrium cancer (group 1, 66 patients), endometrial hyperplasia (group 2, 14 patients), and other reasons besides endometrium cancer (group 3, 20 patients as controls) were included. The cases in the first group were classified by histological type of the cancer, stage, grade, and size of the tumor. In all the cases, expressions of TLRs 2, 4, 5, and 6 were assessed, and the relationship of these receptors with clinicopathologic signs was analyzed. For immunohistochemical staining, nuclear and cytoplasmic stainings were considered positive. A Chi-squared test was used to assess the correlation of the groups. A p<0.05 was considered significant.

Results

The mean ages of patients in groups 1, 2, and 3 were 59.8 (range 33-83), 48.3 (range 40-59), and 53.4 (range 38-84) years, respectively. All types of TLRs were highly expressed in both types of endometrium cancer (groups 1 and 2). TLR expression was observed with a ratio of 87.9% in group 1, 100% in group 2, and 35% in group 3. There was a statistically significant association of TLR 2 among the three groups (p=0.000). TLR 6 expression in both group 1 and group 2 was significantly higher than that in the control group (p=0.000, p=0.000, respectively). In addition, TLR 6 was higher in cases with late-stage cancer (p=0.033). Regarding tumor grade and the size of the tumor, no association was found between TLR 2 and TLR 6.

Conclusion

TLR 2 and TLR 6 were significantly more expressed in cases with endometrium cancer and endometrial hyperplasia. In addition, the presence of TLR 6 may indicate the presence of late-stage endometrial cancer.

Viral Modulation of TLRs and Cytokines and the Related Immunotherapies for HPV-Associated Cancers

The modulation of the host innate immune system is a well-established carcinogenesis feature of several tumors, including human papillomavirus- (HPV-) related cancers. This virus is able to interrupt the initial events of the immune response, including the expression of Toll-like receptors (TLRs), cytokines, and inflammation. Both TLRs and cytokines play a central role in HPV recognition, cell maturation and differentiation as well as immune signalling. Therefore, the imbalance of this sensitive control of the immune response is a key factor for developing immunotherapies, which strengthen the host immune system to accomplish an efficient defence against HPV and HPV-infected cells. Based on this, the review is aimed at exposing the HPV immune evasion mechanisms involving TLRs and cytokines and at discussing existing and potential immunotherapeutic TLR- and cytokine-related tools.

Crosstalk between the HIF-1 and Toll-like receptor/nuclear factor-κB pathways in the oral squamous cell carcinoma microenvironment

Hypoxia is a prominent feature of the microenvironment of solid tumors and may contribute to tumor progression through the oxygen-sensitive transcriptional regulator hypoxia-inducible factor-1 (HIF-1). Chronic inflammation is another typical feature. Inflammatory mediators, including Toll-like receptors (TLRs) and nuclear factor-κB (NF-κB), play an important role in cancer development. Recent studies have revealed extensive cross-talk between hypoxia and inflammation signaling, though the mechanisms remain unclear. Our results confirm that TLR3 and TLR4 are highly expressed in oral squamous cell carcinoma (OSCC). Activation of TLR3 and TLR4 stimulated the expression of HIF-1 through NF-κB. In addition, HIF-1 increased the expression of TLR3 and TLR4 through direct promoter binding. Thus, the TLR/NF-κB pathway forms a positive feedback loop with HIF-1. These results indicate a novel cross-talk between the TLR/NF-κB and HIF-1 signaling, which may contribute to OSCC initiation and progression. With the elucidation of this novel mechanism, it might serve as a basis for future microenvironment targeted cancer therapy.

Toll-like receptor 2 activation implicated in oral squamous cell carcinoma development

Recent studies have revealed that Toll-like receptors (TLRs) are highly expressed and activated in many types of cancer. Physiologically, TLR2 recognizes bacteria and other microorganisms in the oral cavity; however, the role of TLR2 in oral squamous cell carcinoma (OSCC) is unclear. In this study, we demonstrated that TLR2 is highly expressed in OSCC in comparison with adjacent non-malignant tissue. TLR2 was also expressed in OSCC-derived cell lines, and its expression was activated by ligands derived from bacteria and mycoplasma. Furthermore, to elucidate the mechanism of OSCC progression via TLR2 signal transduction, we focused on microRNAs (miRNAs) that are induced by TLR2 activation. Interestingly, ligand activation of TLR2 induced the expression of miR-146a and we found that downregulation of caspase recruitment domain-containing protein 10 (CARD10) mRNA in OSCC-derived cell lines. Moreover, knockdown of CARD10 induced resistance to cisplatin-induced apoptosis in OSCC cells. These findings suggest that the activation of TLR2 by bacterial components can enhance the progression of OSCC and may be implicated in acquired resistance to cisplatin-induced apoptosis through regulation of the miR-146a pathway.

Forkhead box-P3+ regulatory T cells and toll-like receptor 2 co-expression in oral squamous cell carcinoma

BACKGROUND

The function of forkhead box-P3 (FoxP3) regulatory T cells (Treg) and toll-like receptor (TLR)2 protein in the oral cancer microenvironment is not fully understood, but evidence from other malignancies suggests it is likely they are involved with tumour development and progression. The aim of this study was to investigate the distribution of FoxP3⁺cells, TLR2⁺ cells and double-labelled FoxP3⁺TLR2⁺ immune cells in oral squamous cell carcinoma (OSCC), using immunohistochemistry (IHC) and immunofluorescence (IF).

METHODS

25 archival cases of OSCC were immunostained with anti-FoxP3 and anti-TLR2 antibodies. Inflamed hyperplastic oral mucosal tissues were used as controls. The proportion of single-labelled, double-labelled and negative cells was determined.

RESULTS

A higher frequency of double-labelled FoxP3⁺TLR2⁺ Tregs was observed within the immune cells of OSCC compared to inflamed controls using IHC (p<0.05). Cell-to-cell contact between single-stained TLR2⁺ cells and FoxP3⁺ cells was noted. Double IF studies validated demonstration of co-expression of FoxP3⁺/TLR2⁺ immune cells in OSCC.

CONCLUSION

The presence of FoxP3⁺TLR2⁺ cells within the OSCC microenvironment may represent a dendritic cell-dependent pathway capable of inhibiting Treg suppressive activity, potentially enhancing the anti-tumour response. Modulation of TLR2-Treg interactions should be further explored to determine if they have a role in the therapeutic management of OSCC.

Targeting Toll-like receptor 2 inhibits growth of head and neck squamous cell carcinoma

Infection-driven inflammation has been proposed to be involved in the tumorigenesis of head and neck squamous cell carcinoma (HNSCC). Oral HNSCC is often colonized with microbes such as gram-positive bacteria and yeast, where ligands derived from their wall components have been shown to specifically bind to Toll-like receptor 2 (TLR2). Although TLR2 has been described to be expressed in oral HNSCC, its function has not been well characterized. Here, we show the expression of TLR2 in both HNSCC cell lines and primary patient-derived HNSCC xenograft tumors. Activation of TLR2 with a yeast-derived ligand of TLR2, zymosan, promoted organoid formation in an ex vivo model of tumor growth, while blockade with anti-TLR2 antibodies inhibited organoid formation. Zymosan also induced phosphorylation of ERK and the p65 subunit of NF-κB, which was inhibited in the presence of anti-TLR2 antibodies, indicating that this receptor is functional in HNSCC and that the signaling through these pathways is intact. TLR2 blockade also inhibited growth of human xenografted tumors in immunodeficient mice. In summary, our data show that TLR2 is a functional receptor expressed in human HNSCC that plays a direct pro-tumorigenic role, and that it can be therapeutically targeted with blocking antibodies to reduce tumor growth.

Toll-like receptors and cancer, particularly oral squamous cell carcinoma

It is becoming increasingly apparent that the tumor microenvironment plays an important role in the progression of cancer. The microenvironment may promote tumor cell survival and proliferation or, alternatively may induce tumor cell apoptosis. Toll-like receptors (TLRs) are transmembrane proteins, expressed on immune cells and epithelial cells, that recognize exogenous and endogenous macromolecules. Once activated, they initiate signaling pathways leading to the release of cytokines and chemokines, which recruit immune cells inducing further cytokine production, the production of angiogenic mediators and growth factors, all of which may influence tumor progression. This paper examines the actions of TLRs in carcinogenesis with particular emphasis on their role in oral squamous cell carcinoma.

Roles of toll-like receptors in cancer: a double-edged sword for defense and offense

Toll-like receptors (TLRs) belong to a class of pattern-recognition receptors that play an important role in host defense against pathogens by recognizing a wide variety of pathogen-associated molecular patterns (PAMPs). Besides driving inflammatory responses, TLRs also regulate cell proliferation and survival by expanding useful immune cells and integrating inflammatory responses and tissue repair processes. TLR signaling, which is centrally involved in the initiation of both innate and adaptive immune responses, has been thought to be restricted to immune cells. However, recent studies have shown that functional TLRs are expressed not only on immune cells, but also on cancer cells, thus implicating a role of TLRs in tumor biology. Increasing bodies of evidence have suggested that TLRs act as a double-edged sword in cancer cells because uncontrolled TLR signaling provides a microenvironment that is necessary for tumor cells to proliferate and evade the immune response. Alternatively, TLRs can induce an antitumor immune response in order to inhibit tumor progression. In this review, we summarize the dual roles of TLRs in tumor cells and, more importantly, delve into the therapeutic potential of TLRs in the context of tumorigenesis.

Exogenous or endogenous Toll-like receptor ligands: which is the MVP in tumorigenesis?

Toll-like receptors (TLRs) are a class of pattern recognition receptors sensing microbial components and triggering an immune response against pathogens. In addition to their role in anti-infection immunity, increasing evidence indicates that engagement of TLRs can promote cancer cell survival and proliferation, induce tumor immune evasion, and enhance tumor metastasis and chemoresistance. Recent studies have demonstrated that endogenous molecules or damage-associated molecular patterns released from damaged/necrotic tissues are capable of activating TLRs and that the endogenous ligands-mediated TLR signaling is implicated in the tumor development and affects the therapeutic efficacy of tumors. Since both exogenous and endogenous TLR ligands can initiate TLR signaling, which is the most valuable player in tumor development becomes an interesting question. Here, we summarize the effect of TLR signaling on the development and progression of tumors, and discuss the role of exogenous and endogenous TLR ligands in the tumorigenesis.

Differential expression of TLR-2 and TLR-4 in the epithelial cells in oral lichen planus

OBJECTIVE

Oral lichen planus (OLP) is a chronic inflammatory condition of the mucosa mediated by a complex signalling network between the keratinocytes and the sub-epithelial lymphocytes. Since OLP occurs in constantly renewing epithelium continuously exposed to commensals, we hypothesised that the epithelial cell microflora interactions may mediate the persistent inflammation. By virtue of their ability to respond to most oral commensal microorganisms, the toll like receptor-2 (TLR-2) and TLR-4 are the most widely investigated receptors in oral diseases. The overall objective of this study was to investigate the role of TLR-2 and TLR-4 in OLP.

DESIGN

Systemically healthy OLP and control subjects were recruited after obtaining the institutional review board approval. Expression of TLR-2 and TLR-4 proteins and transcripts in the tissue epithelium and in the epithelial cells isolated from saliva were determined by immunohistochemistry and quantitative real-time polymerase chain reaction respectively.

RESULTS

The tissue epithelium and the salivary epithelial cells expressed reduced TLR-2 and increased TLR-4 proteins and transcripts in OLP. The salivary epithelial cells from OLP subjects secreted elevated IL-12. However, upon stimulation with bacterial lipopolysaccharide the epithelial cells from OLP exhibited a mixed Th1 (IL-12) and Th2 (IL-4) response. Presence of dexamethasone significantly reduced inflammatory cytokines in the in vitro stimulated cultures of salivary epithelial cells from OLP subjects.

CONCLUSION

Collectively, our data support a critical role for the host-microbial interactions in the OLP pathogenesis. The potential use of exfoliated oral epithelial cells in saliva for functional analysis exponentially increases its value as biological specimen for clinical research.